In microwave systems such as communication systems, microwave circuitry is often implemented in the form of what is commonly known as a microwave monolithic integrated circuit (MMIC). MMICs are a type of integrated circuit (IC) device that operates at microwave frequencies (1 GHz to 300 GHz). An MMIC device typically performs functions such as microwave mixing, power amplification, low noise amplification and high frequency switching. Inputs and outputs on MMIC devices are frequently matched to the standard 50 ohms.
One function performed by a MMIC device is power amplification. Typically, an MMIC device employs a group of FET based distributed amplifiers to provide broadband amplification. Many high-power RF and Microwave application, i.e. switched PAs, high-level mixers, TR switches, series FET PAs require switching elements that are capable of high voltages and currents, switch in extremely fast times, and are isolated from surrounding structures and devices.
As power and efficiency requirements increase, the problem becomes switching larger devices in shorter times and still maintaining the isolation between devices and supplies. The larger the devices the more internal capacitance from terminal to terminal and also more external capacitance from terminal to ground. Eventually, for very large devices the circuits become un-realizable.
Therefore, it is desirable to provide DC isolation solutions for use in switching circuit topologies which avoid isolation problems with high power output devices and enable independent switching of these high power devices irrespective of the bias condition on their switched terminals.